Hybrid powertrains may improve vehicle fuel economy in a variety of ways. For instance, in some hybrid powertrains, the engine may be turned off at idle, during periods of deceleration and braking, and during periods of low speed or light load operation to eliminate efficiency losses due to engine drag. Captured braking energy (via regenerative braking) or energy stored by one of the motors acting as a generator during periods when the engine is operating is utilized during these engine off periods. Transient demand for engine torque or power is supplemented by the motor/generators during operation in engine-on, electrically variable modes, allowing for downsizing the engine without reducing apparent vehicle performance. Additionally, the engine may be operated at or near the optimal efficiency point for a given power demand. The motor/generators are able to capture vehicle kinetic energy during braking, which is used to keep the engine off longer, supplement engine torque or power and/or operate at a lower engine speed, or supplement accessory power supplies. Additionally, the motor/generators are very efficient in accessory power generation and electric power from the battery serves as an available torque reserve allowing operation at a relatively low transmission numerical speed ratio. The hybrid powertrain must be designed to perform when vehicle operating conditions require high output torque. Relying on torque from the motor/generators to do so may necessitate the use of relatively large motor/generators and/or a large energy storage device.